1. Field
The present disclosure relates to the field of communication technologies, and in particular to a monitoring apparatus and method for an optical signal-to-noise ratio and a receiver.
2. Description of the Related Art
Optical signal-to-noise ratio (OSNR) is an amount directly associated with the performance of a system no matter in a conventional optical communication system with direct detection or in a coherent optical communication system. Hence, much attention has been paid to the study of optical signal-to-noise ratio monitoring technologies.
A conventional measurement method based on a definition of OSNR relies on such conditions as that a noise power spectrum is flat, and there exists a section of band in the spectrum that contains noise but contains no signal. As the increase of an optical communication capacity, a transmission length and transmission rate of a coherent optical communication system are greatly increased than before. More optical nodes will result in more fluctuation in a spectral shape of a noise, and an assumption that optical noises are uniformly distributed in a spectrum is facing more challenges. And at the same time, as channel spacing is greatly reduced, finding a band where signals may be neglected to measure noise power becomes an impractical subject. Hence, measurement of an OSNR in a coherent communication system becomes a new hot spot of studies.
In a practical communication system, besides noises in a transmission link itself, a noise introduced by a nonlinear effect is also contained. As a correlation length of a nonlinear noise itself is very short, view from a frequency domain, a power spectrum of a noise introduced by the nonlinear effect is hard to be differentiated from a white noise of the transmission link itself. Hence, for a general OSNR monitoring method, an estimation value of a noise will be overlarge, hence, an estimation value of the corresponding OSNR will be relatively small, which is disadvantageous to the estimation of the system performance of the whole transmission link.
Currently, a nonlinear compensation algorithm based on digital signal processing may be used to compensate for a nonlinear noise, so as to improve the system performance.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.